830 Journal o f M e d i c i n a 1 Chemistry, 1978, Voi. 21, XCJ.8
Notes
Synthesis and Biologic Distribution of Radioiodinated ,&Adrenergic Antagonistsla Robert N. Hanson,*Ib B. Leonard Holman,l' and Michael A. Davislb D e p a r t m e n t of Radiology, Haruard Medical School, Boston, Massachusetts 02215, and D e p a r t m e n t of Medicinal C h e m i s t r y a n d Pharmacology, College of PharmacS and Allied H e a l t h Professions, Northeastern University, Boston, Massachusetts 021 15. Receiced Nocember I O , 1977 Iodinated analogues 2, 7, and 8 were prepared from propranolol, practolol, and acebutolol in 30-50% yields. Radioisotopic exchange between carrier-free Nalz5Iand the molten iodinated P-adrenergic antagonist yielded the corresponding lZ5I-labeledproduct. The biodistribution in rats, determined at 15 and 60 min postinjection, indicated that the radioiodinated analogues of the cardioselective drugs practolol and acebutolol localized to a greater degree in the liver and heart than the analogue of propranolol. Conversely, ['251]iodopropranolo1(2) was concentrated to a greater extent in the lungs than ['261]iodopractolol(7) or ['251]iodoacebutolol(8). Therefore, lz3I- or I3'I-labeled cardioselective P-adrenergic antagonists, such as 7 or 8, may prove useful as radiodiagnostic agents for the external imaging of the myocardium
The availability of y-emitting radiopharmaceuticals which selectively delineate normal from either ischemic or infarcted myocardium has had a significant impact on the detection and diagnosis of a variety of cardiomyopathies. The clinical usefulness of these agents has been somewhat limited by a number of physical and/or biological properties. The lack of a truly satisfactory agent has led to the examination of drugs which exert their pharmacologic effects upon the heart as potential myocardial imaging agents. The extensive literature on the pharmacologic activity of the competitive 0-adrenergic antagonists upon the cardiovasculature and their strong affinity for myocardial receptors led us to examine the feasibility of using radioiodinated analogues of these compounds as cardioselective radiopharmaceuticals. Several groups of investigators have reported the synthesis of high specific activity lZ5I-labeledB-adrenergic antagonists2 and have demonstrated the highly stereospecific affinity of these agents in vitro for the 0-adrenergic receptors in a variety of tissues, including turkey3 and rat erythrocytes,4 rat cerebral cortex,j rat liver,6 rat myocardium,2band t w o rat glioma cell lines.7 The in vivo binding in mice of [ lZ5I]hydroxybenzylpindolol has been describedS8The agents that have been radioiodinated have been prepared from drugs which are basically nonselective with respect to cardiac (3,)vs. vascular (&) receptors and, therefore, they would not be expected to demonstrate a preference for myocardial tissue.Y Because the chemistry and cardiovascular pharmacology of propranolol,10practolol," and acebutolol'2 have been well documented, we have chosen these drugs as the parent compounds for radioiodination. The differences in pharmacologic effects, which range from little selectivity between 8, and ij2 receptors for propranolol to the high cardioselectivity of practolol, would allow us to explore whether a relationship exists between tissue distribution and biologic activity. Analogues of these drugs, similar to those compounds proposed for radioiodination, have already been synthesized and the preparation of the desired products appears quite feasible. In this paper we report the synthesis and the biologic distribution in rats of three lZ5I-iodinatedanalogues of these &adrenergic antagonists in which the radionuclide is situated distally to the 3oxy-1-(isopropylamino)propan-2-ol pharmacophore. Chemistry. Although a considerable number of propranolol, practolol, and acebutolol analogues have been reported, iodinated derivatives have been notably absent. The synthesis of requisite iodinated compounds was undertaken by utilizing the parent drugs as the starting materials. Direct iodination of propranolol with iodine monochloride in acetic acid13 (Scheme I) afforded the 4'-iodo derivative in 30-40% yields. The position of io0022-2623/78/ 18~l.-0830$01.00/0
Scheme I
I
I
2
Scheme I1
I
H N ~ R ~ 0 3 R=H,R~=CH~ 4 R=CHJC0,RIsC3H~
"2
5 R=H 6 R=CH3C0
3- lodobrnzoyl
C hloridr pH 5.5,5' 0 7 R=H 8 R=CH,CO
dination was determined by the appearance in the NMR spectrum of a pair of doublets for the 2' and 3' protons as well as by the virtual identity of the IR and NMR spectra to those of 4'-chloropropranolol which was synthesized unambiguously from 4-chloro-l-naphthol.'0 The route by which the iodinated analogues of practolol and acebutolol were obtained is shown in Scheme 11. Hydrolysis of the parent drugs gave the 4'-aminophenoxy hydrochlorides 5 and 6 which were subsequently acylated with 3-iodobenzoyl ch10ride.l~ Chromatography of the resulting mixture gave the pure 3-iodobenzanilides 7 and 8 in 35-50% yields. Of the several methods for achieving radioiodine isotope exchange, the direct melt method proved to be the most convenient procedure for these compounds.16i16Heating the iodinated analogue a t its melting point for 2 min in the presence of carrier-free NalZ5Iand a small amount of NazS205gave 35-70 % exchange without significant decomposition of the compound. A chromatographic purification of the reaction mixture gave 60-80% recovery of the desired product (Table I). Thin-layer radiochromatography indicated that greater than 95% of the activity was associated with the desired product. 1978 American Chemical Society
Journal
Notes
of
Medicinal Chemistry, 1978, Vol. 21, No. 8 831
Table I compd
formula
mP, " C
2
CI 6HZONOZI C,,H,,N,OJ cz IH25NZO'lI
128.0-130.0 168.0-170.0 177.5-179.5
7 8 a
Radiochromatogram of crude exchange mixture.
recrystn solvent
radiochemical sp act., changea purity mCi/mmol % ex-
analyses
33 c, H, N , 1 83 C, H, N, 1 38 C, H, N , 1 Radiochromatogram of material used for biological distribution. i-PrOH i-PrOH EtOAc
33 61 75
95 94 96
Table 11. Percent Injected Radioactivity in the Tissues of Rats Following Intravenous Administration of [ 2 s I ~ o p r a n o l o l 1 5 min l h ~~~
~~~
%ID/g liver spleen lung heart stomach kidneys small intestine large intestine muscle fat and fur bones blood thyroid
0.74 i 1.15 i 2.58 i 0.35 i
0.12a 0.13 0.85 0.03
0.98
i
0.19
0.20
i
0.02
0.16 0.12 2.76
i
0.01 0.01 0.17
f
i
%ID/organ 7.30 i 0.52 * 3.90 t 0.26 f 1.99 t 1.83 i 12.98 f 1.41 i 19.67 i 8.82 t 2.52 i 1.87 i 0.06 i
0.63 0.11 1.01 0.02 0.77 0.40 2.28 0.55 1.99 2.75 0.32 0.16 0.01
%ID / or gan
%ID/g
0.66 i 0.60 i 2.01 t 0.19 i
0.15a 0.13 0.63 0.03
0.76
i
0.21
0.10
i
0.01
0.12 0.10 6.85
i i
0.03 0.02 1.17
i
7.08 t 0.40 i 2.78 i 0.16 t 2.24 i 1.58 i 16.23 i 0.91 i 10.71 f 9.69 i 1.84 i 1.44 i 0.14 t
0.76 0.04 0.65 0.02 0.60 0.31 4.30 0.54 2.12 2.22 0.35 0.13 0.02
Average value and standard deviation for four rats. Table 111. Percent Injected Radioactivity in t h e Tissues of Rats Following Intravenous Administration of 1 5 min %ID/g liver spleen lungs heart stomach kidneys small intestine large intestine muscle fat and fur bone blood thyroid
%ID/organ
1 . 7 6 I 0.37O 1 . 3 3 i 0.31 1 . 2 4 i 0.42 0.89 f 0.23
18.94 i 0.80 * 1.89 i 0.64 i 0.71 i 3.45 i 2.45 i 0.56 i 18.27 f 5.87 t 2.93 i 0.79 i 0.10 i
1.82 f 0.50 0.20
i
0.02
0.21 0.06 4.73
i i
0.03 0.01 1.00
f
[I
251ll'ractolol
l h 1.45 0.11 0.36 0.09 0.21 0.64 0.43 0.04 1.64 1.47 0.25 0.06 0.02
%ID/g 1.39 f 1.14 i 1.82 i 0.51 i
0.05a 0.12 0.37 0.07
1.27
i
0.23
0.17
i
0.03
0.18 0.06 3.58
i i i
0.02 0.01 0.13
%ID/organ 15.97 i 0.60 i 2.19 i 0.35 i 0.70 i 2.30 i 5.49 i 0.94 i 15.96 f 7.19 i 2.44 t 0.86 i 0.07 f
2.15 0.06 0.34 0.03 0.22 0.23 l.85 0.22 1.40 1.08 0.19 0.07 0.01
Average value and standard deviation for four rats. Table IV. Percent Injected Radioactivity in the Tissues of Rats Following Intravenous Administration of [ I "I] Acebutolol
lh
1 5 min %ID/g
a
liver 2.40 i spleen 0.97 i lungs 1.63 i heart 0.99 i stomach kidneys 2.80 t small intestine large intestine muscle 0.22 i fat and fur bone 0.22 f blood 0.09 i 6.06 f thyroid Average value and standard deviation
0.31a 0.09 0.19 0.13 0.24 0.04 0.03 0.01 1.25 for four rats.
%ID/organ 20.19 i 0.52 i 1.77 f 0.66 i 1.26 i 4.38 f 9.39 i 2.42 i 16.64 t 7.66 i 2.49 i 1.00 i 0.12 i
Biologic Distribution. The biologic distribution was determined in rats after intravenous administration of the radioiodinated drug (10 pCi, 0.5-1.0 mg/kg). The animals were sacrificed either a t 15-min or 1-h intervals which provided an indication of early as well as delayed distribution of the radioiodinated compounds. Because
1.91 0.09 0.23 0.09 0.39 0.57 0.69 2.00 2.23 0.81 0.33 0.05 0.03
%ID/g 1.59 i 0.60 t 1.27 i 0.58 i
O.2la 0.07 0.24 0.06
1 . 1 6 i 0.23 0.20
i
0.02
0.17 i 0.01 0.06 i 0.02
%ID/organ 12.11 t 0.31 i 1.41 t 0.31 i 1.19 i 1.83 i 15.40 t 1.01 t 14.87 i 6.73 i 1.94 i 0.74 i 0.17 i
2.66 0.06 0.20 0.03 0.19 0.15 3.32 0.17 0.96 0.78 0.17 0.12 0.01
external imaging of a subsequent 1231-or 1311-labeled analogue would reflect the presence of the radioiodine regardless of its association with the drug, no attempts were made to analyze for the presence of radioiodinated metabolites in the blood, urine, or feces. For the same reason, the distribution between free and bound drug in
832 Journal of Medicinal C h e m i s t n , 1978, Vol 21, .Yo b
Notes
for satisfactory imaging. The more rapid blood clearance of the cardioselective radiopharmaceuticals 7 and 8 would permit earlier external visualization compared to 2 . The
extension of this work to the preparation of the lzR1-or '"I-labeled analogues would provide a new class of radiopharmaceutical~for the external visualization of the myocardium in man. Experimental Section General. Melting points were determined on a Thomas-Hoover melting point apparatus and were uncorrected. NMR spectra were measured with a Varian T-60 spectrometer using Me2SO-d6 as the solvent and (CH3)$i as the internal standard. IR spectra were measured with a Perkin-Elmer Model 700 spectrophotometer. Elemental analyses were performed by the Schwarzkopf Microanal.tica1 Laboratory, N.Y., and were within kO.470 of the theoretical values unless otherwise noted. Thin-layer chromatography ITIX) was performed with Eastman-Kodak chromagram sheets. 1 :3181and 13232, with fluorescent indicator. Biologic - . =_ c samples containing radioactivity and radiochromatograms were Figure 1. Selected tissue distribution (7~1D,'gJof '"1 &ancounted in a NaI(T1J -,-well counter. Propranolol hydrochloride tagonists a t 15 min and 1 h. and acebutolol hydrochloride were supplied by Ayerst Laboralories. Inc.. and May and Baker, Ltd., respectively. Chemistry. (~)-3-(4'-Iodonaphthoxy)-l-(isopropylthe plasma was not determined. amino)propan-2-01(2). A solution consisting of propranolol Results and Discussion hydrochloride (5.0 g), iodine monochloride (2.9 g), and glacial acetic acid was heated at reflux for 3 h. After removal of solvent the The biologic distributions in rats of the "jI-labeled residue was purified by column chromatography (AIzO3) and analogues 2 , 7 , and 8 at 15 min and 1 h are shown in Tables tallized from 2-propanol to give the pure product (2.7 g, 41 %), 11-IV. In general, the tissues with the highest concenmp 128.0 -180.0"c. Anal. (Cl6Hz0NO2I) C, H, N, I. trations (%ID/g) of radioiodine were the liver, spleen, lung, ( + = ) - 3 - N-(3-Iodobenzoyl)-4-aminophenoxy]-l-(iso[ heart, kidney, and thyroid. Since the thyroid actively propylamino)propan-2-01 (7). Practolol hydrochloride (3) (1.1 sequesters free iodide from the blood, any [ '251]iodide g ) was deacetylated via the procedure of Basil et t o yield compound 5 which was iodobenzoylated in a pH 5.3 solution a t present in the injected solution or resulting from in vivo 5 ' C . The solution was brought to pH 9 and extracted with CHCI,, deiodination would be accumulated there, yielding an the extract was evaporated, and the residue was crystallized from overestimated value for the concentration of the radio?-propanol to give the pure product (0.8 g. 45% J, mp 168.0-170.0 iodinated analogue actually present. The other organs, " C . Anal. (C,yH2~3T\j,041) C. H, 1,I. such as the stomach and intestines, contained lower (+=)+[ N-(3-Iodobenzoyl)-2-acetyl-4-aminophenoxy]-lconcentrations of the agents while the lowest levels of the (isopropylamino)propan-2-01(8). Employing the same proradioiodinated analogues were found in the muscle, fat and cedure used for 7 , 1.86 g ( 5 mmol) of acebutolol hydrochloride fur, bones, and blood. With the exception of the thyroid. (4) was hydrolyzed and then acylated with 3-iodobenzoyl chloride the concentration of the compounds decreased in all tissues (6.0 mmol) and the product was isolated by column chromatography t o yield. after recrystallization from ethyl acetate, 0.86 between the 15-min and 1-h time periods. The distribution g (34%1, mp 177.5- 179.5 "C. Anal. (C21H25N2041) C, H, N, I. by total organ content. as opposed to tissue concentration, ['"'I]Iodine Isotope Exchange. To 10 mg of the iodinated indicated that the major sites of deposition were the liver, analogue 12, 7 , or 8) in a test tube fitted with a serum stopper small intestine, muscle, and fat and fur, each having greater and N,inlet exit needles were added 1-4 mCi of carrier-free Na'*"I than 5% ID/organ. 12200 ('i/mmol) in 5 pI, of 0.08 N NaOH and 4 WLof Na2S205 Although there were minor differences '2iI-labeled (I,:{ p g / ~ L ) The . sides of the test tube were rinsed with 0.3 mL, practolol and acebutolol analogues 7 and 8 had similar oi methanol and the tube was gradually lowered into a hot oil distributional profiles which differed significantly from bath. The methanol was allowed t o distill under a stream of that of ['z51]iodopropranolo1( 2 ) (Figure 1). These difnitrogen. The residue was then heated for 2 min at a temperature ferences are most apparent in the %ID/g of the radio5 " C greater than the melting point of the analogue. The residue was cooled to ambient temperature, dissolved in 0.5 mL of 2.5% pharmaceutical present in the liver, lung, heart, kidney, MeOH CHCI,. and applied to the top of the alumina column (8.0 and blood. The concentrations of radioiodinated 7 and 8 x 0.5 cni i.d.). The column was eluted with 2.5% MeOH--CHCl, are approximately twice that of 2 in the liver, heart, and and the fractions (0.5 mL) which contained the bulk of the product kidney at 15 min. This relationship is still maintained at were combined and evaporated to dryness under a stream of 1 h in the liver and heart, but the levels in the kidney nitrogen. The exchange ranged from 35 to 75% and the recovery become essentially equal. At 15 min [ 1 2 5 1 ] i o d ~ p r ~ p r a n ~ lfrom ~ l 65 to 80%. The purity of the recovered radioiodinated is present in higher concentrations in the lungs and blood products was determined by 'TLC on alumina (2.5% MeOHthan 7 and 8 and although the blood level of 2 remains CHCl,,)and greater than 95% of the activity was associated with elevated with respect to 7 and 8, the difference in the lung a single component having the same Rf as the unlabeled compound and being coincident with the single LT\' absorbent component. decreases with time. Approximately 3 4 % of the observed activity was associated with As potential myocardial imaging agents, the radioa non-I!V-active component located at the solvent front in either iodinated practolol and acebutolol analogues, 7 and 8, are hyst em. more promising than [ l~I]iodopropranolol(2). The greater Biologic Distribution. The radioiodinated analogues 2, 7 , extraction by the myocardium at 15 min, together with the and 8 were dissolved in 0.2 mL of 0.1 N HCI, buffered to pH 6.5 lower background activity in the lungs, would permit better with 0.1 M phosphate, and diluted to 2 mL with water. The resolution of the cardiac silhouette. Uptake in the liver solutions were filtered through a millipore filter (0.45 p ) and stored is high relative to myocardial uptake and techniques which in the dark a t 4 "C. increase the heart/liver concentration ratio, such as exThe analogues (0.05-0.10 mL) were injected iv into Sprague--Dawley rats (200-250g) and the animals were sacrificed ercise, position, and diet preparation, might be necessary
Journal of Medicinal Chemistry, 1978, Vol. 21, No. 8 833
Notes either 15 min or 1 h after the injection. The organs of interest were removed, weighed, and counted in a NaI(T1) y-well counter. Care was exercised to avoid cross contamination of the samples. Blood (3 mL) was obtained from a vein in the thoracic cavity. The activity that was observed in each organ was converted to percent of the injected dose per organ (%ID/organ) and/or per gram of organ (%ID/g).
Acknowledgment. The authors wish to thank Alice Carmel and Tanya Wisotsky for expert technical assistance. This investigation was supported in part by NIH Grants HL 17739 and GM 18674, ERDA Contract E(11-114115, and HEW Grant RR07143. References a n d Notes (1) (a) Joint Program in Nuclear Medicine, Harvard Medical School, and Northeastern University; (b) Harvard Medical School and Northeastern University; (c) Harvard Medical School. (2) (a) G. D. Aurbach, S. A. Fedak, C. J. Woodard, J. S.Palmer, D. Hauser, and F. Troxler, Science, 186,1223 (1974);(b) T. K. Harden, B. B. Wolfe, and P. B. Molinoff, Mol. Pharmacol., 12, 1 (1976). (3) E.M. Brown, G. D. Aurbach, D. Hauser, and F. Troxler, J . B i d . Chem., 251, 1232 (1976).
(4) M. E. Charness, D. B. Bylund, B. S. Beckman, M. D. Hollenberg, and S. H. Synder, Life Sci., 19, 243 (1976). (5) J. R. Sporn and P. B. Molinoff, J. Cyclic Nucleotide Res., 2, 149 (1976). (6) B. B. Wolfe, T. K. Harden, and P. B. Molinoff, Proc. Natl. Acad. Sci. U.S.A., 73, 1343 (1976). (7) M. E.Maguire, R. A. Wiklund, H. J. Anderson, and A. G. Gilman, J . B i d . Chem., 251, 1221 (1976). (8) D. B. Bylund, M. E. Charness, and S. H. Synder, J. Pharmacol. Exp. Ther., 201, 644 (1977). (9) H.H. Harms, J . Pharmacol. Exp. Ther., 199, 329 (1976). (10) A. F.Crowther and L. H. Smith, J . Med. Chem., 11, 1009 (1968). (11) A. F. Crowther and L. H. Smith, J . Med. Chem., 14, 511 (1971). (12) B. Basil, J. R. Clark, E. C. J. Coffee, R. Jordan, A. H. Loveless, D. L. Pain, and K. R. H. Wooldridge, J. Med. Chem., 19, 399 (1976). (13) V. H. Wallingford and P. A. Krueger, “Organic Syntheses”, Collect. Vol. 11, Wiley, New York, N.Y., 1943,p 349. (14) L. C. Raiford and H. P. Laukelma, J . Am. Chem. SOC.,47, 1121 (1925). (15) H.Elias, C.Arnold, and G. Kloss, Znt. J. Appl. Radiat. Isot., 24, 463 (1973). (16) M. L. Thakur and S. L. Waters, Znt. J . Appl. Radiat. Zsot., 27, 585 (1976).
Diethyl (4bcu,4ca,9acr,9ba)-3,6-Dichlorocyclobuta[ 1,2-b:3,4- blbisbenzofuran9a,9b(4bH,4cH)-dicarboxylate: the Cis,syn Photodimer of Ethyl 5-Chlorobenzofuran-2-carboxylate, a n Analogue Related to the Antilipidemic Drug Clofibrate’s2 Donald T . Witiak,* Howard A. I. Newman, Guiragos K. Poochikian, Stephen W. Fogt, John R. Baldwin, Christine L. Sober, and Dennis R. Feller Divisions of Medicinal Chemistry and Pharmacology, College of Pharmacy and Department of Pathology, College of Medicine, The Ohio State University, Columbus, Ohio 43210. Received December 5, 1977 The antilipidemic properties of diethyl (4bcu,4ccu,9acu,4b~)-3,6-dichlorocyclobuta[1,2-b:3,4-b~bisbenzofuran9a,9b(4bH,4cH)-dicarboxylate,herein termed dimer 8, were studied in sucrose-fedand in Triton-induced hyperlipidemic rats. Whereas clofibrate (0.4mmol/kg) exhibited both anticholesterolemic and antitriglyceridemic activity, dimer 8 showed only antitriglyceridemic properties at the lower dose (0.2mmol/kg) in sucrose-fed rats. Dimer 8 only lowered serum triglycerides levels in Triton WR-1339hyperlipidemic rats, whereas clofibrate lowered both cholesterol and triglyceride levels. In the chronic sucrose-fed model, dimer 8 and clofibrate lowered hepatic HMG-CoA reductase activity and produced significant elevations in several parameters of hepatic drug metabolism. No positive relationship between serum cholesterol lowering and reduction of hepatic HMG-CoA reductase activity was observed by these agents in sucrose-fed rats.
Previous reports from these laboratories have established that the ethyl 5-chloro- and 5-phenyl-2,3-dihydrobenzofuran-2-carboxylate analogues (1 and 2) of clofibrate (3) lowered elevated serum cholesterol levels but had no effect on elevated serum triglyceride concentrations in Triton WR-1339 induced hyperlipidemic rat^.^,^ The converse was true for the unsaturated 5-chlorobenzofuran analogue 4.4
3
‘l,R=Cl 2, R = Ph
CI
4 is structurally similar to either 1 or 4, it was of interest to examine the antilipidemic properties of this compound. In this study we discuss the characterization and pharmacological properties of the photodimer compared with clofibrate in both the acute Triton hyperlipidemic5 and chronic sucrose-fed rat6 models. This study is part of an extensive program designed to utilize clofibrate-related analogues as enzyme and lipid interactive probes in a variety of animal model^.^ The Triton hypertriglyceridemic model presumably reflects inhibition of triglyceride catabolism,6 whereas the sucrose-fed rat model is a reflection of precursor-produced hypertrigly~eridemia.~ Further, chronic administration of aryloxy analogues is required to probe the observable effects on the modification of hepatic microsomal enzymes involved in cholesterol biosynthesis and drug oxidation.lOJ1Investigations of such parameters should provide insight into structural requirements relative to metabolic actions and antilipidemic effects.
Jmfo2-+ 4
Since each half of the cyclobutane “2
+ 2” photodimer of
0022-2623/78/l82l-0833$01.00/00 1978 American Chemical Society
